1. Field of the Invention
The present invention relates to a method of fabricating a temperature control device used for controlling a temperature, for example, of a silicon substrate in the fabrication processes.
2. Description of the Related Art
The processes of fabricating a semiconductor wafer include processes of controlling a temperature of a substrate such as, for example, a baking treatment process of heating the above described substrate in order to remove a remaining solvent in a photoresist film (photosensitive film), which is the surface of a substrate coated, and a cooling treatment process for cooling a heated substrate to the level of room temperature. Therefore, a substrate treatment device used in these treatment processes is equipped with a temperature control device.
FIG. 18 is a side elevation view of a schematic configuration of a temperature control device. A temperature control device 40 is equipped with a temperature control element 41 and a pair of heat conduction plates 42 and 43 disposed on both sides of this temperature control element 41. The temperature control element 41 has a pair of insulating substrates 44 and 45 disposed in opposed positions, electrodes 46 and 47 are formed on the opposing surfaces of these insulating substrates 44 and 45, respectively. A P-type element and a N-type element are connected between the opposing electrodes 46 and 47 by soft soldering as a thermionic element 48. The thermionic element 48 is connected via the electrodes 46 and 47 so that the P-type element and the N-type element are disposed in series in an alternate manner. Therefore, in the temperature control element 41, when the current is flown to the row of the thermionic elements from one direction, one of the insulating substrates, i.e., the insulating substrate 44 is of an endothermic side, and the other insulating substrate, i.e., the insulating substrate 45 is of a radiator side, and when the current flows in the other direction, one of the insulating substrate, i.e., the insulating substrate 44 is a of radiator side, the other insulating substrate, i.e., the insulating substrate 45 is of an endothermic side. It should be noted that a pair of heat conduction plates 42 and 43 are disposed on the outside surfaces of the respective insulating substrates 44 and 45 in order to enhance the responsiveness and the heat homogeneity of the temperature control element 41.
FIG. 19 is a processing diagram for illustrating a conventional fabrication of a temperature control device. First, in the process S1, the electrode 46 is formed on the surface of one of the two insulating substrates, i.e., the insulating substrate 44. The electrode 46 is formed by etching for example, a copper plate pasted on the surface of the insulating substrate 44. Next, in the process S2, cream soft solder is printed on the predetermined position of the surface of the formed electrode. Then, in the process S3, one terminal of the thermionic element 48 is mounted in the location where the cream soft solder is printed.
On the other hand, in the process of S4, the electrode 47 is formed on the surface of the other insulating substrate 45. The electrode 47 is formed by etching a copper pasted on the surface of the insulating substrate 45 similarly to the above described process S1. Then, in the process S5, a cream soft solder is printed on the predetermined location of the formed electrode surface.
Subsequently, in the process S6, a pair of insulating substrates 44 and 45 are aligned in order to perform soft soldering of the thermionic element 48 and the electrodes 46 and 47. The alignment is carried out so that the other terminal of the thermionic element 48 is contacted with the cream soft solder of the surface of the electrode of the other insulating substrate 45 as well as the insulating substrates 44 and 45 are disposed so that the electrodes 46 and 47 are opposed each other. Then, in the process S7, these are heated to a temperature more than the temperature of the fusing point of the soft solder, for example, on the order of 200° C. and the soft soldering of the thermionic element 48 and the electrodes 46 and 47 are carried out.
Subsequently, in the process of S8, grease is coated on the outer sides of a pair of insulating substrates 44 and 45, respectively. Coating the grease promotes the enhancement of the heat conductivity property such as the responsiveness of the temperature control and the heat homogeneity of the surface of the heat conduction plate by enhancing the adhesion and the heat conductivity between the insulating substrates 44 and 45 and the heat conduction plates 42 and 43. Then, in the process S9, the heat conduction plates 42 and 43 are disposed on the outer sides of a pair of insulating substrates 44 and 45 while making the grease layers stand therebetween, thereby completing the temperature control device 40.
In the process S7 of soft soldering of the above described thermionic element 48, a slight load is added to the direction of a pair of insulating substrates 44 and 45 getting closer to each other in order to prevent the defect of soft soldering and the deviation of location. However, if the load is too slight, since the thickness of soft solder layers generates the variations, the flatness which is important to enhance the heat conduction property cannot be secured. Particularly, in the case where the thickness of the insulating substrates 44 and 45 are made thinner, since the insulating substrates 44 and 45 are easily deformed, and the lowering of the flatness is significant.
On the other hand, if the load is made heavier in order to homogenize the thickness of soft soldering, the melting soft soldering is flown out to the circumference of the site of soft soldering, the thickness of soft solder layer cannot be secured, and the strength of the soft soldering is lowered. Hence, the technology that the thickness of the soft solder layer is secured by employing the soft solder mixed with copper powder, and the strength of the soft soldering is secured has been proposed (see Japanese Unexamined Patent Publication No. Hei 6-290819 gazette; Japanese Unexamined Patent Publication No. Hei 1-17839 gazette). However, in the case where soft solder mixed with copper powder is used, the problem that the flatness can not be maintained occurs.
Moreover, when the heat conduction plates 42 and 43 are disposed, it is necessary to rub the heat conduction plates 42 and 43 and the insulating substrates 44 and 45 together following coating a grease on the insulating substrates 44 and 45. However, it is difficult to add the heavy load in a uniform manner if the coating area of the grease is large. Therefore, the problem that the variations of the thickness of grease layers is generated and the flatness which is crucial for enhancing the heat conduction property cannot be secured. Moreover, since bubbles incorporated within the grease at the time when the grease is coated remains as those are, the problem that the variations of heat conduction rate is generated occurs. Still further, the problem that the tendency of the thickness of a grease layer is thickened by the remaining bubbles and the heat conduction rate is lowered also exists.
Furthermore, if the processing precision is enhanced and the flatness of them has been finely fabricated previously at the time of the fabrication of the insulating substrates 44 and 45 and the heat conduction plates 42 and 43, they can be nestled within the allowance range even if the flatness is degraded by the variations of the thickness of soft solder layers and grease layers. However, if the processing precision of machinery is enhanced, the problem that the cost of processing increases largely and the cost of fabrication is higher will occur.